The present invention relates to a bonding apparatus and method and more particularly to a bonding apparatus and method for executing a bonding process after performing a surface treatment on a bonding subject
Bonding apparatuses are generally for making connections between chip electrode units and circuit board lead terminals with fine metal wires. Chip electrode units connected by fine metal wires are sometimes called bonding pads, and circuit board lead terminals are sometimes called bonding leads. When fine metal wires are connected to these using ultrasonic connection technology or thermo-compression bonding or the like, it is important to know surface conditions thereof. More specifically, when the surface of either the metal layer of a bonding pad or the metal layer of a bonding lead is contaminated, or foreign matter is present thereon, it is not possible to obtain a good electrical junction between such surface and the fine metal wire, and the strength of the mechanical junction is also weak.
For that reason, one thing that is proposed is that the metal layer be protected beforehand. In Japanese Patent Application Laid-Open Disclosure (2000) No. 2001-15549, for example, a semiconductor device is disclosed, and effecting a multi-layer structure in a bonding wire connection electrode pad in a semiconductor device in which wiring materials of copper or a copper alloy are used is discussed. More specifically, a concavity is formed on a semiconductor substrate, and, in that concavity, from the lower layer, a copper film 16, a diffusion preventing film 17, and an oxidation preventing film 18 are formed, in that order. Furthermore, a copper-based anchor layer 13, 15 that contacts the lower surface of the copper film is imbedded in the insulating film layer 12 of the semiconductor device. The diffusion prevention layer is either TiN or W or the like, while the oxidation preventing film is an alloy the main component thereof is Al, Au, or Ag, or the like. All of these are formed in the concavity, and the diffusion preventing film and oxidation preventing film deposited on portions other than that are removed by chemical-mechanical polishing (CMP); as a result, an electrode pad of the same height as the insulating film is obtained.
Another thing that is tried is to subject the bonding pad or bonding lead to a surface treatment prior to performing the bonding processing. In Japanese Patent Application Laid-Open Disclosure (2000) No. 2000-340599, for example, an apparatus, among others, for effecting wire bonding after cleaning the surface to be connected are disclosed, and a wire bonding apparatus 12 integrally comprised of a plasma jet unit 50 and a wire bonding unit 51 is described therein. The plasma jet unit has a concentric double structure comprising an outer dielectric tube 23 and an inner dielectric tube 22. A grounded conical electrode 27 is provided in the outer dielectric tube, and a rod-shaped high-frequency electrode 26 is provided in the interior of the inner dielectric tube, respectively, and, therebetween, after introducing, for example, argon gas an intra-atmospheric glow discharge is induced, and a low-temperature plasma is generated. The plasma generated in this manner is ejected from a gas ejection port, exposed on an electrode on a BGA board, contamination thereupon is removed, and, thereafter, wire bonding is performed.
Japanese Patent Application Laid-Open Disclosure (1999) No. H11-260597, which is corresponding to U.S. Pat. No. 6,429,400 B1 discloses a plasma processing apparatus, among others, are disclosed, and the cooling of electrodes 3 and the outer electrode 1 and the like are described therein as a method of suppressing streamer discharges in order to perform a plasma process by a stabilized glow discharge. A system using this plasma processing apparatus, as described therein, performs surface treatments on a plurality of bonding pads enclosing electronic components on IC-mounted circuit boards transported by a belt conveyor. It is further described that the coordinates of the bonding pads of the boards are read in, the jetting position of a plasma jet is controlled according to those coordinates, and, by sequential feeding, only the bonding pads are subjected to plasma processing.
In Japanese Patent Application Laid-Open Disclosure (2003) No. 2003-328138, a microplasma CVD apparatus is disclosed. In this apparatus, a high-frequency coil 7 is provided at the narrowed tip of a tubular plasma torch 5 formed of an insulating material 3, and a wire passes through the inside of the plasma torch; and in this structure, induction plasma is induced by high-frequency electric power between the high-frequency coil and the wire inside the plasma torch. It is farther described that the diameter at the tip of the plasma torch is about 100 μm, and, thereby, in a 200 μm or so area, materials such as graphite and glassy carbon are deposited in the atmosphere using a high-density microplasma.
Of the conventional technologies in which bonding pads or bonding leads are subjected to a surface treatment prior to bonding processing, the technologies treated in Japanese Patent Application Laid-Open Disclosure (2000) Nos. 2000-340599 and H11-260597 employ gas that is being a plasma by a glow discharge. This method is a capacitively coupled plasma generating method, and it involves electrical discharges; accordingly, there would be damage to electronic devices. As a result, there are limitations in applying this method to objects that are thereafter very difficult to anneal, as with bonding processing.
The technology of Japanese Patent Application Laid-Open Disclosure (2003) No. 2003-328138, furthermore, uses an induction plasma induced by a high-frequency coil and hence belongs to the so-called inductively coupled plasma generation methods. Inductively coupled plasma, in general, is a hot plasma, and, with the high plasma temperature as is, electronic devices are damaged. The microplasma technology of Japanese Patent Application Laid-Open Disclosure (2003) No. 2003-328138 discloses stably generating this hot plasma in an extremely narrow space; and in this technology, small, limited areas are irradiated with plasma, and little thermal damage wilt be done. From these facts, it is considered possible to use the microplasma technology of Japanese Patent Application Laid-Open Disclosure (2003) No. 2003-328138 in surface treatment prior to bonding processing.
For wire bonding apparatuses, meanwhile, the current demands for higher precision and higher speed are strong, and, in the movement of bonding heads for holding wires and performing bonding processes, high-precision positioning is performed at high speed, Accordingly, in order to perform surface treatment prior to bonding processing, the unique demands of such a bonding apparatus made to operate at high speed must be taken into consideration. Japanese Patent Application Laid-Open Disclosure No. H11-260597 and No. 2003-328138 do not give consideration to the relationship with bonding processing, and, in Japanese Patent Application Laid-Open Disclosure (2000) No. 2000-340599, no specific content for an integrated configuration for a plasma jet unit and a wire bonding unit is discussed.
As seen from the above, with bonding apparatuses in the conventional art, it is very difficult to efficiently perform surface treatment and bonding processing on bonding subjects. Bonding subject surface treatments can be largely divided between removal processes and deposition processes. In surface removal processes, foreign matter such as an oxidized film and organic matter or the like on the surface of bonding subjects is removed by oxidation, reduction, or etching or the like, making surface of the boding subjects clean. In deposition processes, a material exhibiting good bonding qualities, such as gold that is the same as the bonding wire, for example, is deposited on the surface of the bonding subject Material removal and deposition are possible with conventional microplasma technology described above, but what is yet to be resolved is how to employ that in bonding technology.